This paper reports further findings from an ongoing clinical study designed to evaluate the extent to which pH values of aspirates from feeding tubes can be used to differentiate between gastric and intestinal tube placement and gastric and respiratory tube placement. The sample consisted of 405 aspirates from small-bore nasogastric tubes and 389 aspirates from nasointestinal tubes, which were obtained from 605 subjects ranging in age from 18 to 94 years. Data were collected at the time of initial placement and again, when possible, after feedings were initiated. A total of 794 pH-meter readings were made concurrently with X-rays to determine feeding tube position. Gastric placement was successfully distinguished from intestinal placement of the feeding tubes on the basis of pH-meter readings (p < .0001). Approximately 85% of the 405 pH-meter readings from gastric fluid were between 0 and 6.0, while over 87% of the 389 pH-meter measurements performed on intestinal aspirates were greater than 6.0. Four aspirates from feeding tubes inadvertently placed in the respiratory tract (two in the pleural space and two in the tracheobronchial tree) were tested with a pH-meter, all had pH values greater than 6.5.